Imaging, therapy, and temperature monitoring ultrasonic method

ABSTRACT

An ultrasonic system useful for providing imaging, therapy and temperature monitoring generally comprises an acoustic transducer assembly configured to enable the ultrasound system to perform the imaging, therapy and temperature monitoring functions. The acoustic transducer assembly comprises a single transducer that is operatively connected to an imaging subsystem, a therapy subsystem and a temperature monitoring subsystem. The ultrasound system may also include a display for imaging and temperature monitoring functions. Additionally, the acoustic transducer assembly can be configured to provide three-dimensional imaging, temperature monitoring or therapeutic heating through the use of adaptive algorithms and/or rotational or translational movement. Moreover, a plurality of the exemplary single transducers can be provided to facilitate enhanced treatment capabilities.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/744,655, filed May 4, 2007 and which is U.S. Pat. No. 8,480,585,which application is a continuation of U.S. patent application Ser. No.10/193,419, filed on Jul. 10, 2002 and which is now U.S. Pat. No.7,229,411, which application is a continuation of U.S. patentapplication Ser. No. 08/950,353 filed on Oct. 14, 1997 and which is nowU.S. Pat. No. 6,050,943, and is also a continuation-in-part of U.S.patent application Ser. No. 09/502,174, filed on Feb. 10, 2000 and whichis now U.S. Pat. No. 6,500,121, all of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to a non-invasive therapeuticultrasonic system, and more particularly, to a system which is capableof acoustically imaging and heating a certain region to be treated (“thetreatment region”) in target tissue for therapeutic purposes as well asacoustically monitoring the temperature profile of the treatment region.

2. Description of the Related Art

The absorption of energy in tissue, for example, in the human bodyproduces an increase in temperature, which can be exploited fortherapeutic purposes. The irradiation of ultrasound to the target tissuesuch as in the human body, which has been successfully used for decadesmainly in increasingly sophisticated diagnostic imaging applications,also allows the target tissue to absorb a certain amount of energy.Thus, ultrasound may be used in the therapeutic uses.

Specifically, ultrasonic energy at frequencies above 1.5 MHZ has anacoustic wavelength less than 1 mm in the human tissue. This energy iseasily controlled in beamwidth and depth of penetration, and has afavorable absorption characteristic in the tissue. These aspects allowthe energy to be precisely localized such that regions may beselectively heated while sparing overlying tissue structures.

Ultrasound has significant advantages for therapeutic applications ascompared to micro-wave radio-frequency (RF) energy or optical energy(laser light).

In contrast with the ultrasound, the RF energy is characterized by longwavelengths in the tissue, with limited to poor control of energydeposition, and high absorption.

These aspects of the RF energy constrain its therapeutic usage to largesuperficial areas. On the other hand, the optical energy which istypically emitted from lasers can be precisely controlled in beamwidth,but the opacity and high absorption in the tissue also limits its use tosurface treatment or invasive procedures. Furthermore, the laser and RFenergy are emitted from ionizing radiation sources which are typicallyassociated with some risk, unlike acoustic transducers which aretypically used for generating ultrasound.

However, in contrast with the diagnostic uses, the therapeutic uses ofultrasound such as hyperthermia and non-invasive surgery have seenrelatively little progress due to several technological barriers.

The primary impediment has been a lack of the ability to monitortemperature in the treatment region during the therapeutic treatmentprocess.

Specifically, one of objectives of the therapeutic application is tocreate a very well-placed thermal gradient in the target tissue toselectively destroy certain regions thereof. For example, hyperthermiatechnique typically requires to maintain the tissue temperature nearabout 43 degrees Celsius, while the goal of non-invasive surgery istypically to elevate the tissue temperature above and beyond about 55degrees Celsius. Moreover, during the therapeutic treatment process, thephysiological response of the target tissue is directly related to thespatial extent and temporal duration of the heating pattern.Consequently, in order to appropriately perform feedback and control ofthe therapeutic treatment process for obtaining successful results, itis absolutely essential to monitor the temperature in the target tissue,for example, so as to know whether or not the temperature in thetreatment region has been raised to a level that produces a desiredtherapeutic effect or destruction in the tissue. In addition, it ispreferable to know the temperature distribution in the treatment regionand the vicinity thereof for enhancing the therapeutic effect.

In the conventional technique, the therapeutic ultrasonic system hastypically relied upon thermocouple probes for monitoring the temperaturein the treatment region and the vicinity thereof. However, thethermocouple probes are highly invasive because they have to be insertedinto the region-of-interest. In addition, use of the thermocouple probeshas necessarily led to very poor spatial resolution since only a smallnumber of probes could be safely embedded in the region-of-interest.Furthermore, the thus embedded thermocouple probes are likely to disturbthe acoustic propagation in the tissue and typically cause excessiveheating at the probe interface during the therapeutic treatment process.This results in undesirably modified temperature distribution as well aserroneous measurements.

Another factor which has curtailed progress in the therapeutic uses ofultrasound has been the design of the conventional acoustic transducers.

In general, for the therapeutic treatment process, imaging of thetreatment region is necessary to determine the location of the treatmentregion with respect to the acoustic transducers as well as to evaluateprogress of the treatment process.

Such essential functions of imaging as well as the aforementionedtemperature monitoring may be implemented with the same acoustictransducer to be used for the therapeutic purposes, since the acoustictransducers can actually produce an image of the region-of-interest byemploying well-established imaging technique such as B-scan imaging.However, the conventional acoustic transducers which are typicallyemployed for the therapeutic purposes are acoustically large, oftensingle-element devices having narrow bandwidth in the frequency domain.Although they are designed to efficiently transmit acoustic energy tothe target tissue, the conventional acoustic transducers are typicallyunsuited for imaging of the treatment region and/or monitoring thetemperature profile therein. This precludes development andimplementation of these vital functions for performing a desirableprecise therapeutic treatment process.

Some prior art references teach the use of ultrasound for therapeuticpurposes. For example, U.S. Pat. No. 4,757,820 to Itoh discloses anultrasound therapy system having functions of imaging and heating thetarget using ultrasound beams for the therapeutic purposes. The systemdisclosed therein, however, does not have the temperature monitoringfunction.

U.S. Pat. No. 5,370,121 to Reichenberger et al. discloses a method andan apparatus for non-invasive measurement of a temperature change in asubject, in particular a living subject, using ultrasound waveforms. Themethod and apparatus disclosed therein, however, relies on adifferential ultrasound image between two successive ultrasound imagesof the target. In other words, any temperature change is detected as atemperature-induced change in brightness between the two images, whichappears in the differential image. Consequently, an actual real-timemonitoring of the temperature may be difficult in the disclosed methodand apparatus. Moreover, although the method and apparatus can detectchanges in the temperature of the target, an absolute value of thetarget temperature may not be obtained therefrom. In addition, anymovement of the target may introduce changes in the differential image,which may cause erroneous results.

Furthermore, although it is not distinctly intended to be applied in thetherapeutic treatment process for the target tissue such as in the humanbody, U.S. Pat. No. 5,360,268 to Hayashi et al. discloses an ultrasonictemperature measuring apparatus in which a temperature of the target,medium is calculated using a propagation time of ultrasonic waves whichpropagated for a predetermined distance in the target medium. Theapparatus disclosed therein, however, is mainly described as employingseparate ultrasonic elements which respectively function for atransmitter and a receiver of the ultrasonic waves.

While some prior art temperature monitoring techniques exist, see, forexample, U.S. Pat. No. 4,807,633 issued to Fry on Feb. 28, 1989, suchtechniques are complex and have limited applicability. That is, use ofsuch techniques essentially preclude use of the system for purposes ofimaging, unless one were to use multiple transducers. In that regard,while two or more physically separated transducers can be used toaccomplish imaging and therapy, typically with one configured forimaging and the other for therapy, such a system is susceptible to thegeneration of imprecise data and is overly complex and expensive.

Thus, it would be advantageous to provide a compact, non-invasive systemcapable of acoustically performing the therapeutic heating and theimaging of the treatment region in the target tissue as well as thetemperature monitoring in the treatment region with a single acoustictransducer. Moreover, it would also be advantageous to provide acompact, non-invasive system capable of performing three-dimensionalimaging, temperature monitoring and therapeutic heating of the treatmentregion to provide a more focused therapeutic treatment process.

In other applications, it would be advantageous to provide therapeuticultrasonic systems with multiple transducers capable of facilitating theimaging, temperature monitoring, and therapeutic heating functions toobtain imaging and temperature information over a larger area of theregion-of-interest and provide therapeutic heating more appropriately tothe target tissue, for example, over a larger region-of-interest, withan increased intensity at the treatment region, or more readily focusedtowards the target tissue.

SUMMARY OF THE INVENTION

In accordance with various aspects of the present invention, anon-invasive therapeutic ultrasonic system is provided, which features asingle acoustic transducer and some other subsystems capable ofacoustically performing therapeutic heating and imaging of the treatmentregion as well as acoustically monitoring, the temperature profile inthe treatment region and the vicinity thereof. Also disclosed herein isa system architecture and associated components as well as algorithmswhich can be implemented to acoustically achieve the heating, imaging,and temperature monitoring functions. The imaging and monitoringfunctions allow precise feedback and control of the therapeutictreatment process so that the therapy can be conducted moresuccessfully. In addition, because a single transducer is utilizedperfect correspondence is obtained; that is, image artifacts and/orimprecise registration difficulties yielded through use of multipletransducers can be avoided.

A novel acoustic transducer disclosed herein is capable of generatinghigh acoustic power for the therapeutic treatment process, while at thesame time providing a good imaging function. Specifically, in order toobtain good lateral resolution in the imaging process, the acoustictransducer of the present invention is preferably divided into an arrayof sub-elements, each processing acoustic waves with a sufficientbandwidth for good axial resolution in the imaging process.

These imaging requirements are also extended to the acoustic temperaturemonitoring function of the treatment region. In accordance with variousaspects of the present invention, an acoustic temperature measurementsubsystem disclosed herein is capable of non-invasively mapping thetemperature distribution or profile in the target tissue in real-time.This feature is accomplished by measuring the time-of-flight andamplitude data of acoustic pulses through the region-of-interest whileexploiting the temperature dependence of the speed of sound and acousticattenuation in the target tissue. The acoustic nature of this processallows the same acoustic transducer which is used for the imaging andtherapy functions to be used for the real-time temperature monitoringfunction. Alternatively, the use of the multiple acoustic transducersallows the temperature mapping to be conducted with a higher spatialresolution. The thus gathered valuable information on the temperature inthe target tissue can be used to achieve precise control of the spatialdistribution of heating, detailed knowledge of the heating duration, andquantitative temperature data during the therapeutic treatment process,which has not been previously possible in the conventional art.

In accordance with other aspects of the present invention, the acoustictransducers disclosed herein can be configured to providethree-dimensional imaging, temperature mapping and therapeutic heatingof the treatment region.

These three-dimensional features may be realized by any number ofmethods, such as, for example, the use of adaptive algorithms or the useof mechanical scanning devices.

Additional aspects of the present invention may include the ability toprovide therapeutic ultrasonic systems with multiple transducers capableof facilitating the imaging, temperature monitoring, and therapeuticheating functions to obtain imaging and temperature information over alarger area of the region-of-interest and provide therapeutic heatingmore appropriately to the target tissue, for example, over a largerregion-of-interest, with an increased intensity at the treatment region,or more readily focused towards the target tissue.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred exemplary embodiments of the present invention is described inconjunction with the appended drawing figures in which like numeralsdenote like elements, and:

FIG. 1 is a cross-sectional view of an acoustic transducer assemblyaccording to the present invention;

FIG. 2 is a diagram of an imaging subsystem interfaced to the acoustictransducer assembly according to the present invention;

FIG. 3 is a diagram of a therapy subsystem interfaced to the acoustictransducer assembly according to the present invention;

FIG. 4 is a diagram illustrating a temperature monitoring subsystemaccording to the present invention;

FIG. 5 depicts waveforms of heated and unheated states illustrating thetime shift and amplitude change of the echo in the region of interest;

FIG. 6 is a diagram of a further embodiment of a temperature monitoringsubsystem interfaced to the acoustic transducer assembly according tothe present invention;

FIG. 7 is a depiction of the intersecting paths of acoustic rayspossible from a transducer source;

FIG. 8 illustrates a tomographic configuration useful in connection withyet another embodiment of a temperature monitoring subsystem accordingto the present invention;

FIGS. 9A-D show the characteristics of an exemplary transducer made inaccordance with various aspects of the present invention;

FIGS. 10A-B show, respectively, the pulse echo waveform and thefrequency spectrum of the echo of an exemplary transducer made inaccordance with various aspects of the present invention;

FIG. 11 is a diagram of an exemplary embodiment of an ultrasonic systemhaving three-dimensional imaging and temperature monitoringcapabilities;

FIG. 12 is a diagram of another exemplary embodiment of an ultrasonicsystem having additional capabilities for providing imaging andtemperature monitoring over a region-of-interest;

FIG. 13 is a diagram of yet another exemplary embodiment of anultrasonic system having multiple transducers; and

FIG. 14 is a diagram of an exemplary embodiment of a two dimensionalimaging array.

DETAILED DESCRIPTION

A system for achieving successful ultrasonic therapy procedures inaccordance with the present invention includes four major subsystems orcomponents. Specifically, they are an acoustic transducer assembly, animaging subsystem, a therapy subsystem (also referred to as a“therapeutic heating subsystem”), and a temperature monitoringsubsystem, which are illustrated in FIGS. 1 through 4, respectively.Although not shown in the drawing figures, the system further includescomponents typically associated with a therapy system, such as anyrequired power sources, memory requirements, system control electronics,and the like.

With reference to FIG. 1, the acoustic transducer assembly 100 includedin the system of the present invention will be described in detailbelow. As shown in the cross-sectional view of FIG. 1, the acoustictransducer assembly 100 includes a piezoelectric ceramic plate 10. Theair-backed side of the ceramic plate 10 is partially diced to have aplurality of curved (e.g. concave) portions 15 to form a linear arraystructure. The thickness of the diced ceramic plate is selected toprovide a center frequency for example from 500 kHz to 20 MHZ, withlower frequencies yielding deeper penetration and higher frequenciesproviding greater resolution. The concave portions 15 constituting thetransducer array are spaced to achieve good lateral resolution in theimaging function. On the face of each of the concave portions 15, ametal electrode 20 is provided to connect the ceramic plate 10 to thesystem control electronics (not shown in the figure) via a cable 30 anda terminal 40. The other face of the ceramic plate 10 is configured suchas to receive a common metal electrode 25. The common electrode 25 isalso connected to the system control electronics via a cable 35 and aterminal 45.

In addition, although a concave portion is described above, it shouldalso be noted that portion 15 may also comprise a substantially flatconfiguration with a natural locus arrangement, e.g., without a focusinglens. Moreover, portion 15 can also be configured with a substantiallyflat configuration having a convex or concave lens arrangement.Accordingly, portion 15 may be configured in various manners withoutdeparting from the scope of the present invention.

The phrase “air-backed” means that there is no backing material providedon the back side of the acoustic transducer assembly 100, unlike thetypical conventional acoustic transducers. Specifically, theconventional acoustic transducers are typically provided with some kindsof the backing layer typically made of a loaded epoxy, such as analumina powder epoxy. The loaded particles in the backing layer,however, introduces increased acoustic impedance as well as providingscattering surfaces therein. Accordingly, when the generated acousticwaves come to the backing layer and hit the loaded particles includedtherein, the particles tend to disburse the acoustic waves in differentdirections into the epoxy matrix so that attenuation increases. As aresult, the operational efficiency of the acoustic transducer decreasessince some portion of the generated acoustic energy is absorbed in thebacking layer. On the other hand, in the acoustic transducer assembly100 of the present invention, by providing no backing layer on the backend of the ceramic plate 10, the acoustic waves are reflected withoutbeing absorbed there to propagate toward the target tissue, resulting inthe increased efficiency.

Alternatively, a certain backing layer may be provided as long as it hasa very low acoustic absorption so that any significant absorption of thegenerated acoustic energy does not happen.

On the common electrode 25, one or more acoustic matching layers 50 isbonded using an adhesive such as an epoxy. When a loaded epoxy is usedas the adhesive, the acoustic matching layer 50 can be simply castthereon since they adhere naturally to each other. The acoustic matchinglayer 50 is intended to obtain appropriate impedance matching betweenthe ceramic plate 10 and the target tissue. Consequently, efficienttransfer of acoustic power from the ceramic plate 10 to the targettissue can be maintained to achieve an appropriate temperature increasein the target tissue, resulting in desired therapeutic results. When theacoustic matching layer 50 (or layers) is bonded to the ceramic plate 10(precisely, to the common electrode 25) with a loaded epoxy, theacoustic impedance can be easily adjusted by changing the amount ofmetal particles loaded in the epoxy.

At the same time, acoustic matching layer(s) 50 can increase thebandwidth of the emitted acoustic waves in the frequency domain. Thisaspect is suitable for the effective imaging function.

Specifically, in order to improve the sensitivity in the imagingfunction, it is preferable that the emitted acoustic waves are verypulsive in the time domain since acoustic pulses with a very short pulsewidth can produce clearly distinct echoes from different interfacesexisting in the target tissue. The shorter the width of the acousticpulses is, the more clearly the distinct echoes can be resolved,resulting in improved resolution in the obtained images. The short pulsein the time domain means a wide range in the frequency domain whichcovers a large spectrum. On the other hand, however, when considering anefficient transmission of the acoustic energy from the acoustictransducer assembly 100 to the target tissue which is important for thetherapeutic treatment process, it is preferable to use stable acousticwaves such as “continuous waves” or gated bursts, which in turn meansthat the bandwidth thereof in the frequency domain is narrow. Thus,trade-off between the efficiency in the therapeutic function and thesensitivity in the imaging function has to be satisfied by appropriatelysetting the bandwidth of the acoustic waves to be emitted.

Without acoustic matching layer(s) 50, the bandwidth of the emittedacoustic waves is determined mainly based on the design of the ceramicplate 10 which actually generates the acoustic waves. This results inthe limited degrees of freedom for adjusting the bandwidth. Providingone or more acoustic matching layer(s) 50 makes it possible to properlyadjust the bandwidth in a wide range without substantially changing thedesign of the ceramic plate 10.

Typically, the thickness of the acoustic matching layer 50 is set to beon the order of a quarter of a wavelength, of the acoustic waves. Inaddition, it is preferable that the acoustic impedance of the acousticmatching layer 50 be set to be approximately equal to the square root ofthe acoustic impedance of the ceramic plate 10 times the acousticimpedance of the target tissue or, more preferably, the acousticimpedance of the ceramic plate raised to the .THETA. power, times theacoustic impedance of the target tissue raised to the K power. Also,multiple matching layers may be used, of course, with suitable changesin layer impedances.

The acoustic matching layer 50 can be made of various types ofmaterials, such as ceramics, plastics, metals and a composite materialthereof. Preferably the matching layer may exhibit good thermalconductivity and low acoustic attenuation.

Matching layer (or layers) 50 may be cut or diced, such as shown on FIG.1, to maintain high acoustic isolation, i.e., low acoustic crosstalk.However, any heating of the matching layer(s) of ceramic may becontrolled via the duty cycle of the drive signal or via active orpassive cooling methodologies. In addition, any other conventionalcooling technique and/or methodology may be utilized.

Although not shown on FIG. 1, it should be appreciated that transducerassembly 100 may be provided with a back layer (not shown) suitablyconfigured to modify the bandwidth of the transducer and/or serve as aheat sink.

The ceramic plate 10 and other related components configured as setforth above are coupled to the target tissue via a fluid 70 circulatingbetween the acoustic matching layer 50 and an acoustically-transparentmembrane 60. The fluid 70 also functions as a coolant for the ceramicplate 10 and the acoustic matching layer 50 and may also aid incontrolling the temperature of the tissue at the interface.

Temperature control via a circulating fluid, thermoelectric coolingmodule and/or pneumatic or other devices may also be utilized inaccordance with various aspects of the present invention. Furthermore,the acoustic transducer assembly 100 having the aforementionedconfiguration is enclosed in a water-tight housing (not shown in thefigure).

The circulating fluid 70 has two major functions as mentioned above. Oneof them is to couple the ceramic plate 10 and the acoustic matchinglayer 50 to the target tissue. The other is to remove the waste heataway from the acoustic transducer assembly 100. In particular, theenergy conversion efficiency of the acoustic transducer assembly 100 istypically about 80%, and consequently, some portion of the inputelectrical power becomes the waste heat. When a large amount ofelectrical power is input to the acoustic transducer assembly 100, theassembly 100 is heated up. This may result in reduced efficiency andaltered operational characteristics, which are likely to produce adverseeffects on the therapeutic purposes. The circulating fluid 70 thereforekeeps the acoustic transducer assembly 100 at a stable and constanttemperature by cooling it off.

The fluid 70 is typically water. Alternatively, any suitable mineraloil, plant oil, or other suitable liquid could be used as the fluid 70.

With reference to FIG. 2, an imaging subsystem 200 which is interfacedto the acoustic transducer assembly 100 is described below. The imagingsubsystem 200 connected to the acoustic transducer assembly 100 via acable 210 includes a beam forming control unit. The unit is operated sothat the acoustic transducer assembly 100 scans the region-of-interest,including the treatment region, in the target tissue 800 with theacoustic waves. The returning acoustic signal is received by theacoustic transducer assembly 100, and then sent to the imaging subsystem200 to generate ultrasonic images of the treatment region. The thusgenerated image is displayed on a video display terminal 500 to assistthe user in appropriately positioning the acoustic transducer assembly100 with respect to the treatment region in the target tissue 800 priorto actually commencing the therapeutic treatment process.

With reference to FIG. 3, a therapy subsystem (a therapeutic heatingsystem) 300 which is interfaced to the acoustic transducer assembly 100is described below.

The therapy subsystem 300 connected to the acoustic transducer assembly100 via a cable 310 includes power RF drivers which are interfaced tothe linear array of the acoustic transducer assembly 100, i.e., to eachof the respective portions 15 of the ceramic plate 10 shown in FIG. 1.The power RF drivers are also connected to the common electrode 25provided on the other face of the ceramic plate 10. By appropriatelyapplying RF signal voltages to the ceramic plate 10 from the thusconnected power RF drivers, high power acoustic energy is generated. Thedrivers are controlled in-time so that the acoustic transducer assembly100 transmits, steers, and/or focuses the acoustic waves to theregion-of-interest including the treatment region in the target tissue800. Heating power and heating time as well as transducer anodizationare all controlled during the therapeutic treatment process to achievethe proper heating pattern and therapeutic dosage. The control can besupplemented by the feedback of information from the temperaturemonitoring subsystem described later.

In connection with yet another embodiment of the present invention,temperatures are monitored in a manner calculated to avoid tissue motionartifacts. For example, in the case where a localized region is heated,in accordance with this embodiment of the present invention, the heatedregion is interrogated with a pulse echo signal substantiallyimmediately thereafter. In such a case the echo from the heated regionwill be changed in time and amplitude. For example, the acousticattenuation in tissue approximately doubles from 50° C. to 70° C.Preferably, the region is measured immediately before and after heatingand thus, tissue motion artifacts are avoided, as well as any acousticpropagation effects.

In the case where only a small region is treated at a time, anisothermal region about the hot spot is engendered. Therefore, thetime-of-flight and the amplitude of wave incident on the heated regionis the same before and after the therapeutic energy is delivered. Thus,the amplitude change and time change measured after therapy will be duesubstantially to the tissue treated.

With reference to FIG. 4, a general schematic utilizing this approach isshown where transducer assembly 100 is used to heat a small region 800.As shown, the temperature monitoring subsystem 400 is connected todisplay 500.

Temperature monitoring subsystem 400 is also connected to transducerassembly 100, such as by a suitable cable 410. In accordance with thisaspect of the present invention, the whole volume is scanned, and bysweeping the pulse echo the effective thermal dose (time/temperaturehistory) (e.g. recrossed volume) can be determined. In the context ofthe present invention the term thermal dose relates to the temperatureand time of duration integral function by which, for example, adetermination of necrosity can be made.

With reference to FIG. 5, the echo waveform in a windowed region of awaveform A obtained before heating and a waveform B after heating can beexamined, and based on the time-duration and spatial extent of theheated area, i.e. the time shift of the echo in the heated region andtissue and thermal properties, the temperature can be determined.

Alternatively, instead of evaluating the time shift, the echo amplitudein the windowed region could be examined. In accordance with this aspectof this embodiment of the present invention, when the amplitude of thesignal in the windowed region begins to rapidly fall, the temperaturewill be in the 50° C. to 70° C. range. In this manner the effectivenecrosed volume can be determined.

It should be appreciated that in accordance with various aspects of thepresent invention, both echo time shifts and amplitude changes may beemployed. For example, by scanning the windowed region in one, two, orthree dimensions, a temperature map or image can be obtained.

Of course this technique may also be performed on an incremental basisto compensate for changes in temperature along some line, including, forexample, before/after the hot spot. For example, by windowing outregions from the transducer to the region of interest and in each regioncomputing the temperature from attenuation techniques or phase shifts, atemperature profile can be accurately determined.

With reference to FIG. 6, a temperature monitoring subsystem 400 whichis interfaced to the acoustic transducer assembly 100 and monitor 500 isdescribed below. The temperature monitoring subsystem 400 connected tothe acoustic transducer assembly 100 via a cable 410 includes a controlunit. The unit is operated so that the temperature mapping process asfollows is properly conducted.

In particular, an acoustic pulse wave is first generated by a singletransmitting element 110 among the linear array of the acoustictransducer assembly 100. The thus generated acoustic pulse wavepropagates into the target tissue 800 and through any temperaturegradients. Since the speed of sound in the target tissue 800 exhibitstemperature dependency, the acoustic wavefronts will be sped up orslowed down in certain regions based on the temperature gradientsexisting in the target tissue 800. Upon reaching a boundary 850 used forreference the acoustic wavefronts are reflected thereon so that thereflected wavefronts, i.e., the echoes come back towards the acoustictransducer assembly 100, where they are detected by remaining elements120 in the linear array. Upon the echoes returned from the target tissue800 are detected by the acoustic transducer assembly 100, a certainsignal is sent to the temperature monitoring subsystem 400 in which thetime-of-flight data of the detected echoes (i.e., the returned acousticwavefronts) which is a period of time required from the emission of acertain acoustic pulse to the detection of the corresponding echo (thereflected acoustic wave) is calculated. The abovetransmitting-and-detecting sequence is repeated for each uniquetransmitter-receiver combination to form a large data set.

Finally, using propagation path data, the obtained time-of-flight datais numerically converted into speed data of sound in the target tissue,and then further into a matrix of temperature values. Specifically, thespeed V of sound (in this case, the speed of the ultrasonic wave) in thetarget tissue is expressed as follows:V=Vo+f(T)  (1)where Vo represents the speed of sound at a certain temperature in thetarget tissue, T is a temperature of the target tissue, and f(T) is afunction of T. Furthermore, the speed V of sound is also expressed asfollows:V=L/t  (2)where L represents the length of the propagation path while t representsthe propagation time (i.e., the time of flight) which is required thrthe sound (i.e., the acoustic wave) to cover the propagation path of thelength L.

As a result, from the above-mentioned expressions (1) and (2), thetemperature T of the target tissue can be calculated based on themeasured time-of-flight (the propagation time) data t with using valuesfor L, Vo and f(T). Typical values for Vo and f(T) are known in the artor readily measured in experiments. On the other hand, the propagationpath length L for the above calculation can be determined in severalmanners.

For example, a small biopsy needle, typically metallic, with a squarecross-section can be placed in the target tissue until reaching apredetermined depth. Such a metallic needle provides a large amount ofreflection of the acoustic waves, thereby functioning an artificialreference boundary placed at the predetermined known depth in the targettissue.

Alternatively, instead of providing the artificial boundary, any naturalboundaries existing in the target tissue can be used as the referenceboundary which provides the basis of calculating the propagation pathlength. Such natural boundary will include a tissue-to-air boundary, atissue-to-water boundary, a tissue-to-bone boundary, and the like.

When any actual artificial or natural boundaries are not available inthe target tissue as the reference boundary, an imaginary boundary or avirtual boundary can be produced. When one acoustic pulse or wave isemitted toward the target tissue at a time of zero (0) and thecorresponding returning echo is detected at a time of X, then thespecific pulse or wave has traveled in the target tissue over a distancewhich is approximately calculated as X times the speed of sound. Thus,the signal processing and analysis in the subsequent processes can beconducted based on this particular echo as the reference.

Analogous to the time-of-flight data, and use thereof as describedherein, in accordance with various aspects of the present invention, theamplitude of the returned echos can also be used to create an image ofthe acoustic attenuation.

The obtained temperature data is sent to the video display terminal 500for visualization by the user, and also sent to the therapy subsystem300 previously described for dynamic control of the heating process forthe therapeutic treatment purposes.

In accordance with yet another embodiment of the present invention,temperature can be monitored using a tomographic approach (in additionto FIG. 6 embodiment). With reference to FIG. 7 the intersecting path ofa transducer 100 having multiple elements is illustrated. The path ofpropagation is determined by the diffraction of the source and theproperties of the medium. Along a path s the acoustic time-of-flight, Twill be the integral of the incremental delays over s

$\begin{matrix}{T = {\int\frac{\mathbb{d}s}{v(s)}}} & (3)\end{matrix}$It should be appreciated that the acoustic propagation will consist ofphase retardation (additional delay) and diffraction loss (amplitudeloss), refraction, and various tissues with associated speed of soundcharacteristics, and each of these factors can, if desired, be includedin the analysis.

In any event, by considering the intersecting paths, such as shown inFIG. 7, superimposed over a grid of pixels, where each pixel representsan area (volume) a tomographic configuration shown in FIG. 8 isobtained. By tracing the propagation and reception of the rays asolution to the velocity in each pixel from the matrix can be calculatedaccording to the following equation:[T]=[ds][1/v]  (4)where [T] is a vector of measured delays, [ds] a matrix of knowndistances and [1/v] a vector of slowness, the reciprocal of the speed ofsound (and thus temperature) in each pixel. Given the dependence of thespeed of sound in tissue with temperature, the spatial temperaturedistribution in each pixel is thus determined.

As noted briefly above, other factors including acoustic diffraction(beam spreading) and the temperature coefficients of tissue can beincorporated to enhance the accuracy of this method. In accordance witha particularly preferred aspect, as will be described in more detailbelow, the array can be rotated to allow for a three-dimensional imagingas well as a map of temperature to be measured.

By measuring the ray paths and then heating the region and rapidlyre-measuring an accurate spatial map of heating is obtainable, such mapbeing substantially free of tissue motion artifacts.

As described above, the ultrasonic therapy system of the presentinvention includes an acoustic transducer assembly (in other words, theacoustic transducer subsystem), a therapy subsystem (in other words, atherapeutic heating subsystem), and a temperature monitoring subsystemas well as an appropriate display and control interface. Thisarchitecture non-invasively provides essential functions of real-timeimaging and temperature monitoring of the treatment region during thetherapeutic treatment process. This enables the user to obtain thefeedback of the results of the therapeutic treatment process, resultingin improved, control of the process. By using the disclosed system ofthe present invention, safe, automated, and well-controlled proceduresfor the therapeutic treatment process are achieved, at low cost and inonly seconds or minutes of therapy. The use of the disclosed transducercapable of imaging, therapy, and monitoring allows precise geometricplacement and monitoring of lesions, which has not previously beenpossible with prior art systems and/or methodologies.

With reference to FIGS. 9A-D and 10A-B, the performance of a transducermade in accordance with the present invention will now be described.Specifically, a 5×5 mm therapy transducer has been constructed inaccordance with the present invention and the characteristics of thattransducer determined.

With respect to FIG. 9A, for example, the power versus frequency plotshown therein shows the electrical input, acoustical output and heatloss curves, respectively. As will be appreciated, each of these aspectsare well within desirable ranges. Similarly, and with reference now toFIG. 9B, the transmit efficiency of the transducer over the range of 3-4MHZ is on the order of above 80%, which, as will be appreciated by thoseskilled in the art, is more than acceptable. It should be appreciatedthat any suitable frequency range could be utilized.

Referring now to FIG. 9C, the voltage, current and impedance magnitudeof the transducer over a similar frequency range (e.g., 3-4 MHZ) isshown. In accordance with this particular embodiment, the drive voltageis on the order of about 30 volts, the current on the order of about 400milliamps, and the impedance magnitude on the order of about 70 ohms.

Finally, with respect to FIG. 9D, the acoustical power at high poweroutputs is shown, and, as such, it can be seen that as electrical poweris increased, the heating efficiency drops. However, over acceptableranges, transducers made in accordance with the present inventionexhibit acceptable performance.

Referring now to FIG. 10, the pulse echo waveform of the aforementionedexemplary transducer is shown in FIG. 10A and the frequency spectrum ofthe echo, without electrical tuning, is shown in FIG. 10B. As will beappreciated by those skilled in the art, the frequency spectrum and echovoltage plots evidence the usability and functioning of transducers madein accordance with the present invention. Specifically, it will be notedthat the transducers exhibit high fractional bandwidth. Although thespecific transducer used in gathering the data shown in FIG. 10comprises a transducer with a single matching layer and no electricaltuning, providing two or more matching layers, as noted above, andelectrically tuning the transducer may enhance such characteristics toover 50% or more.

As discussed above, a need exists for therapeutic ultrasonic systems tofurther provide enhanced imaging and treatment capabilities, such asthree-dimensional imaging and temperature information, andthree-dimensional therapeutic heating. In that regard, a combinedimaging, therapy and temperature monitoring system comprising a singleacoustic transducer 100 can be configured to provide a three-dimensionalsystem and thus facilitate enhanced imaging and treatment capabilities.In accordance with this aspect, the three-dimensional system can providevolumetric information relating to the target tissue 800. Byfacilitating three-dimensional imaging and temperature monitoring of thetarget tissue 800, the three-dimensional system enables medicalpractitioners to more readily ascertain the location, as well as thedepth, of the treatment region. Accordingly, with the enhanced imagingand temperature monitoring of the treated region, therapeutic heatingcan be concentrated within a more specific area of the target tissue800, thus resulting in improved therapeutic results.

Continuing in accordance with this aspect of the invention, thethree-dimensional imaging, therapy and temperature monitoring system canbe configured in various manners depending upon the particularapplication as well as various cost considerations. For example, thethree-dimensional system can comprise a single acoustic transducer 100configured to provide only three-dimensional imaging, three-dimensionalmapping of temperature, or three-dimensional therapeutic heating of thetreatment region. Further, the three-dimensional system can be suitablyconfigured to provide both three-dimensional imaging andthree-dimensional temperature mapping, or may include either featurewith three-dimensional therapeutic heating. In accordance with apreferred aspect of the invention, the single acoustic transducer 100 isconfigured to provide all three features, i.e., three-dimensionalimaging, therapy and temperature monitoring.

In accordance with another aspect of the invention, the singletransducer 100 can be suitably diced to form a 1-dimensional array, suchas is described above.

Additionally, the single transducer 100 can be suitably diced intwo-dimensions to form a two-dimensional array. For example, withreference to FIG. 14, an exemplary two-dimensional array 1400 can besuitably diced into two-dimensional portions 1402. The two dimensionalportions 1402 can be suitably configured to focus on the treatmentregion at a certain depth, and thus provide respective slices 1404 ofthe treatment region. As a result, the two-dimensional array 1400 canprovide a two-dimensional slicing of the image plane of a treatmentregion 1406.

To provide three-dimensional imaging, temperature monitoring andtherapeutic heating of the target tissue 800, the three-dimensionalsystem can comprise a single acoustic transducer 100 configured with anadaptive, algorithm, such as, for example, three-dimensional graphicsoftware, contained in a control subsystem, such as, for example, theimaging subsystem 200, the therapeutic subsystem 300 or the temperaturemonitoring subsystem 400. The adaptive algorithm is suitably configuredto receive two-dimensional imaging and temperature information relatingto the region-of-interest, process the received information, and thenprovide corresponding three-dimensional imaging and temperatureinformation.

In accordance with this aspect of the invention, the three-dimensionalsystem suitably comprises a two-dimensional array 1400 to providetwo-dimensional information to the control subsystem. Accordingly, theadaptive algorithm may suitably receive slices 1404 from different imageplanes of the treatment region, process the received information, andthen provide volumetric information 1406, e.g., three-dimensionalimaging and temperature information. Moreover, after processing thereceived information with the adaptive algorithm, the two-dimensionalarray 1400 may suitably provide therapeutic heating to the volumetricregion 1406 as desired.

Alternatively, rather than utilizing an adaptive algorithm, such asthree-dimensional software, to provide three-dimensional imaging ortemperature information, the three-dimensional system can comprise asingle transducer 100 configured to operate from various rotationalpositions relative to the target tissue 800. In accordance with thisaspect of the invention, the single transducer 100 may be suitablyconfigured in a one-dimensional array or a two-dimensional array, suchas array 1400. For example, with reference to FIG. 11, the singletransducer 100 can be configured to rotate around a perimeter 1104 ofthe treatment region to provide three-dimensional imaging andtemperature information. Moreover, the single transducer 100 can beconfigured to rotate around an axis 1102 to provide three-dimensionalinformation. Still further, the single transducer 100 can be configuredto translate or sweep along an axis 1103 to provide a largerfield-of-view and thus facilitate additional three-dimensionalinformation. The rotational movement can comprise movement in either aclockwise or counterclockwise direction, or both. Further, therotational movement could include complete or partial rotations. Thus,the rotational movement could include movement between only twopositions, or between any other number of rotational positions.Accordingly, the three-dimensional system 1100 may comprise a singletransducer having any rotational and/or translational arrangementsuitably configured to provide three-dimensional information.

Moreover, the movement of the single acoustic transducer 100 in variousrotational and/or translational positions can be controlled by anymechanical scanning device now known or hereinafter devised forautomated movement.

However, the rotational movement of the single acoustic transducer 100may also be controlled by manually placing the acoustic transducer 100in various desired, rotational positions.

Still further, while the three-dimensional system may include a singleacoustic transducer configured with a two-dimensional array 1400 and anadaptive algorithm to provide three-dimensional imaging, temperaturemonitoring and therapeutic heating to a treatment region 1406, thethree-dimensional system may be configured to include both an adaptivealgorithm and rotational and/or translational movement to provideadditional information. As such, an even larger area of treatment may beobtained through the use of both the adaptive algorithm and therotational and/or translational movement.

Continuing with this example, the three-dimensional system can besuitably configured to capture imaging and temperature information andprovide therapeutic heating from the acoustic transducer 100 once thetransducer 100 becomes fixedly maintained at various rotationalpositions. Further, the three-dimensional system can also be suitablyconfigured to capture imaging and temperature information and providetherapeutic heating just prior to, or just after, becoming fixedlypositioned. Moreover, the three-dimensional system can be configured tocapture imaging and temperature information and provide therapeuticheating during movement around the various rotational positions.

Having obtained imaging and temperature information corresponding to athree-dimensional representation of the treatment region within thetarget tissue 800, whether through the use of an adaptive algorithm,such as three-dimensional software, rotational movement of the acoustictransducer, or both, improved therapeutic treatment can be facilitatedby the imaging, therapy and temperature monitoring system 1100.Moreover, imaging and temperature information can be accumulated toprovide three-dimensional representation of the image and temperaturewithin the treatment region which enables the system 1100 to morereadily ascertain the location and depth, as well as temperature of theregion-of-interest. Still further, based on the three-dimensionalinformation, the system 1100 can be suitably automated if desired toprovide therapeutic treatment to a selected volume within theregion-of-interest.

In accordance with another embodiment of an ultrasonic system forproviding therapeutic treatment, a single ultrasonic probe may beprovided which includes at least two acoustic transducers configuredwithin the probe. In accordance with this exemplary embodiment, at leastone of the acoustic transducers is configured to facilitate imaging,temperature monitoring and therapeutic heating for a treatment region.With reference to FIG. 12, an exemplary embodiment of such an ultrasonicsystem 1200 is shown.

In accordance with this exemplary embodiment, the ultrasonic system 1200suitably comprises a single probe 1202 having at least two acoustictransducers 1204 and 1206. The single probe 1202 comprises anyconventional probe configured for having multiple transducers within. Inthe exemplary embodiment, the probe 1202 comprises a cylindricalendoscope. However, the probe 1202 may also comprise a catheter or acystoscope and the like. Additionally, as will be described in moredetail below, the single probe 1202 may be rotatably connected to theultrasonic system 1200 to permit rotational movement of the acoustictransducers 1204 and 1206. Moreover, although only two acoustictransducers 1204 and 1206 are shown, the single probe 1202 may suitablyinclude any number of acoustic transducers.

The acoustic transducers 1204 and 1206 are suitably configured withinthe probe 1202 to provide imaging, temperature monitoring andtherapeutic treatment of the treatment region. Notably, at least one oftransducers 1204 and 1206 comprises a single transducer 100 forproviding imaging, temperature monitoring and therapeutic heating, atleast one of transducers 1204 and 1206 can facilitate all threefunctions, imaging, temperature monitoring and therapeutic heating.Moreover, each transducer 1204 and 1206 may separately provide imaging,temperature monitoring and therapeutic heating. In addition, transducers1204 and 1206 may be configured with various ranges of operating,frequency, such as, for example, between 1 to 18 MHZ or more.

In accordance with another aspect of the invention, transducers 1204 and1206 are suitably configured in different positional orientations withinprobe 1202. In accordance with the exemplary embodiment, the transducers1204 and 1206 are suitably configured in substantially opposingdirections. Accordingly, transducers 1204 and 1206 can providerespective fields-of-view (image or treatment planes) 1208 and 1210which represent separate regions-of-interest. Moreover, by rotatingprobe 1202, for example, such as by rotational movement 1212, eachtransducer 1204 and 1206 can provide either field-of-view 1208 or 1210,or various fields-of-view in between.

Although the fields-of-view 1208 and 1210 are shown as separateregions-of-interest, the transducers 1204 and 1206 may also be suitablypositioned within the probe 1202 such that the fields-of-view 1208 and1210 suitably overlap. Accordingly, the ultrasonic probe 1202 of theexemplary embodiment can suitably provide simultaneous operation withintwo regions-of-interest, or can provide sequential operations within thesame region-of-interest. Moreover, as a result of the above rotationalconfigurations, three-dimensional imaging and temperature informationcan also be readily obtained. Still further, by operating transducers1204 and 1206 simultaneously, the imaging, temperature monitoring, andtherapeutic heating can be suitably provided over a larger area of thetarget tissue if desired.

In accordance with another aspect of this exemplary embodiment, thetransducers 1202 and 1204 may be suitably configured with differentoperating frequencies. Thus, transducer 1202 may be configured for highfrequency imaging, for example, between 12 to 18 MHZ, while transducer1204 may be configured for low frequency imaging, for example, between 3to 5 MHZ. Moreover, transducer 1202 may be configured for low frequencyimaging while transducer 1204 is configured for high frequency imaging.By having such different frequencies, particularly if operatingsimultaneously, transducers 1202 and 1204 can suitably providecapabilities of both high frequency, which facilitates high resolutionimaging, and low frequency, which easily controls beamwidth and depth ofpenetration. Accordingly, an ultrasonic probe can be realized whichprovides a wider range of imaging information.

In accordance with another embodiment of an ultrasonic system forproviding therapeutic treatment, an extracorporeal probe, for example,one outside the body, having at least one acoustic transducer may beincluded with an endoscopic or cystoscopic probe and the like, forexample, one proximate to the target tissue, also having at least oneacoustic transducer. Further, both probes are suitably oriented suchthat the respective transducers are configured to operate onsubstantially the same treatment region. As a result, therapeuticheating can be focused towards the treatment region in a manner thatprovides increased intensity. In accordance with this exemplaryembodiment, at least one of the acoustic transducers is configured tofacilitate imaging, temperature monitoring and therapeutic heating for atreatment region. With reference to FIG. 13, an exemplary embodiment ofsuch an ultrasonic system 1300 is shown.

In accordance with this exemplary embodiment, the ultrasonic system 1300suitably comprises a extracorporeal probe 1302 and an endoscopic probe1304.

The extracorporeal probe 1302 suitably comprises any conventional, probeconfigured for external or non-invasive use. Accordingly, the singleextracorporeal probe 1302 is suitably configured outside a body region1312, for example, proximate a bodily surface 1310. Meanwhile, thesingle endoscopic probe 1304 suitably comprises any conventional probe,such as, for example, endoscopic, cystoscopic, or catheter-based probeand the like, configured for invasive use proximate to a target tissue800. Accordingly, the single endoscopic probe 1304 is suitablyconfigured within a body region 1312 and proximate the target tissue800. Moreover, although only a single acoustic transducer 1306 and 1308are respectively shown for the probes 1302 and 1304, any number ofacoustic transducers may be included within the probes 1302 and 1304.

The acoustic transducers 1306 and 1308 are suitably configured withinthe probes 1302 and 1304, respectively, to provide imaging, temperaturemonitoring and therapeutic treatment of the treatment region. Notably,at least one of transducers 1306 and 1308 comprises a single transducer100 for providing imaging, temperature monitoring and therapeuticheating. Moreover, each transducer 1306 and 1308 may separately provideimaging, temperature monitoring and therapeutic heating. In addition,transducers 1306 and 1308 may be configured with various ranges ofoperating frequency, such as, for example, between 1 to 18 MHz or more.As a result, the ultrasonic system 1300 can obtain multiple amounts ofinformation from probes 1302 and 1304 regarding the imaging andtemperature monitoring of a desired treatment region within the targettissue 800, while also providing an increase in the intensity of thetherapeutic treatment of the treatment region.

The present invention has been described above with reference to variousexemplary embodiments. However, those skilled in the art will recognizethat changes and modifications may be made to the exemplary embodimentswithout departing from the scope of the present invention. For example,the various transducers, probes and other components may be implementedin alternate ways, or may be comprised of different materials andthicknesses, depending upon the particular application or inconsideration of any number of performance criteria associated with theoperation of the system. Further, the number of transducers and probesconfigured within the various exemplary embodiments is not limited tothose described herein. In addition, the techniques described herein maybe extended or modified for use with other modes of ultrasonic therapyin addition to the therapeutic heating system of the exemplaryembodiments. These and other changes or modifications are intended to beincluded within the scope of the present invention, as expressed in thefollowing claims.

The invention claimed is:
 1. A method for therapeutic treatmentcomprising the steps of: providing an ultrasonic therapy systemcomprising a single ultrasound transducer, a display, and a controlinterface; and operating the control interface to control the singleultrasound transducer to non-invasively provide imaging of a targetedtissue below a skin surface, provide temperature monitoring of thetargeted tissue, and provide therapeutic heating of the targeted tissue,such that the imaging, the temperature monitoring, and the therapeuticheating are conducted through the use of the single ultrasoundtransducer.
 2. The method according to claim 1, further comprisingproviding feedback from the temperature monitoring temperature of thetargeted tissue, and controlling the therapeutic heating of the targetedtissue based on the feedback.
 3. The method according to claim 1,further comprising moving the single ultrasound transducer along theskin surface to provide an increased amount of the target tissue.
 4. Themethod according to claim 3, further comprising providing the imaging,the temperature monitoring, and the therapeutic heating of the increasedamount of the target tissue.
 5. The method according to claim 1, whereinthe imaging of a targeted tissue below a skin surface provides athree-dimensional image of at least a portion of the targeted tissue. 6.The method according to claim 1, further comprising moving the singleultrasound transducer to form an increased amount of the target tissue,and damaging the increased amount of the target tissue.
 7. The methodaccording to claim 1, wherein the single ultrasound transducer providesa center frequency in a range from 500 kHz to 20 MHZ.